What Is Cement? Manufacturing, Composition & their Functions

What Is Cement? Manufacturing, Constituents & their Functions

Material with adhesive and cohesive  properties. Any material that binds or unites  – essentially like glue

Function Of Cement

1. to bind the sand and coarse aggregate together
2.  to fill voids in between sand and coarse  aggregate particle
3.  to form a compact mass

Types of Cement

2 types of cement normally used in building industry are as follows:

1. a) Hydraulic Cement
2. b) Nonhydraulic Cement

Hydraulic Cement

Hydraulic Cement sets and  hardens by action of water. Such as Portland Cement

In other words it means that hydraulic  cement are:

“ Any cements that turns into a solid product  in the presence of water (as well as air) resulting in a material that does not disintegrate in water.”

Non-hydraulic Cement

Any cement that does not require water to transform it into a solid product.

2 common Non-hydraulic Cement are

1. a) Lime – derived from limestone / chalk
   b) Gypsum
   Portland Cement – constituents of cement

Chemical composition of Portland Cement:

1. a) Tricalcium Silicate (50%)
2. b) Dicalcium Silicate  (25%)
3. c) Tricalcium Aluminate (10%)
4. d) Tetracalcium Aluminoferrite (10%)
5. e) Gypsum (5%)

Functions of Tricalcium Silicate

1. Hardens rapidly and largely responsible for initial set & early strength
2.  The increase in percentage of this compound will cause the early strength of Portland Cement to be higher.
3. A higher percentage of this compound will produces higher heat of hydration and accounts for faster gain in strength.

Functions of Dicalcium Silicate

1. Hardens slowly
2. It effects on strength increases occurs at ages beyond one week .
3. Responsible for long term strength

Functions of Tricalcium Aluminate

1. Contributes to strength development in the first few days because it is the first compound to hydrate .
2. It turns out higher heat of hydration and contributes to faster gain in strength.
3. But it results in poor sulfate resitance and increases the volumetric shrinkage upon drying.
4. Cements with low Tricalcium Aluminate contents usually generate less heat, develop  higher strengths and show greater resistance to sulfate attacks.
5. It has high heat generation and reactive with   soils and water containing moderate to high sulfate concentrations so it’s least desirable.

Function of Tetracalcium Aluminoferrite

1. Assist in the manufacture of Portland Cement by allowing lower clinkering temperature.
2.  Also act as a filler contributes very little strength of concrete eventhough it hydrates very rapidly.
3.  Also responsible for grey colour of Ordinary Portland Cement

Manufacturing Of Portland Cement

The 3 primary constituents of the raw  materials used in the manufacture of  Portland Cement are:

1. a) Lime
   b) Silica
   c) Alumina

Lime is derived from limestone or chalk

Silica & Alumina from clay, shale or bauxite

There are 2 chief aspects  of the manufacturing process:

 First
To produce a finely divided mixture of raw materials – chalk / limestone and clay / shale

Second

To heat this mixture to produce chemical composition

There 2 main process that can be used in manufacturing of Portland Cement that is

1. i) wet process        ii) dry process

WET PROCESS